The present invention relates to a vibration sensor including a pressure sleeve.
German Published Patent Application No. 44 03 660 discusses a vibration sensor having a pressure sleeve which is used with knock sensors for monitoring the function of an internal combustion engine. This pressure sleeve is attached fixedly via a contact area to the component whose vibration is to be detected, in this case to the engine block of the combustion engine.
The vibration to be detected is the knocking sound of the engine during operation with this arrangement, the sound being transmitted via the pressure sleeve to a piezoceramic disk as the actual sensor element with contact disks and insulating disks in between them which permit signal pick-up, thus generating an electric output signal suitable for analysis.
The type of mounting or clamping of this sensory system on the pressure sleeve and the mounting of the vibration sensor on the vibrating component have a great influence here on the method of manufacture as well as any false measurements and disturbances in operation. The clamping of the sensor element having a plurality of individual parts, e.g., with a spring and a seismic mass, is accomplished in this vibration sensor with a threaded ring, for example, which may be screwed onto a corresponding thread on the pressure sleeve.
In addition, a vibration sensor is also discussed in German Published Patent Application No. 195 24 147, in which the threaded ring and the spring in the form of a spring head nut are described as a one-piece component. This spring head nut may then be screwed onto the thread on the pressure sleeve and is thus in direct contact with the seismic mass.
A vibration sensor including a pressure sleeve in which the pressure sleeve is mountable under pressure with an initially concave base area on a component that is the source of vibrations may be provided in an exemplary embodiment of the present invention with a seismic mass with an internal thread that may be screwed onto the sensory system to produce the axial prestress.
In an exemplary embodiment of the present invention, it may be possible to mount a knock sensor on the engine block of an internal combustion engine inexpensively, because fewer individual parts may be needed and, in particular, a lower overall axial height and a lower weight of the vibration sensor may be feasible. Furthermore, omission of the plate spring, which may be present in the known arrangement, may also permit a more constant characteristic curve in detection of the sensor signal.
In a design of the vibration sensor having an injection-molded plastic housing around the pressure sleeve having a sensory system and the seismic mass, the seismic mass may have at least two grooves running radially opposite one another according to an exemplary embodiment of the present invention. Through these grooves the plastic may enter an interior space between the sensory system and the pressure sleeve during extrusion, thereby securing them, so this may permit a compact arrangement that may be mounted in any position, e.g., on the engine block.
In another exemplary embodiment having an injection-molded plastic housing, the sensory system may have at least two grooves running radially opposite one another. Through these grooves, the plastic may enter the interior space between the sensory system and the pressure sleeve during injection. Here again, any desired installation position may be possible, but it may be simpler and less expensive to manufacture a seismic mass without grooves. In both exemplary embodiments, the grooves may be provided on the two axial boundary surfaces of the seismic mass or the piezoceramic disk of the sensory system. They may be offset by 90xc2x0 between one face and the other.
An especially good effect may be achieved in clamping the sensor element with the seismic mass if one or both axial boundary surfaces of the seismic mass are designed to be concave so that the axial wall thickness of the seismic mass may become smaller toward the center.
A vibration sensor in which a base area of the pressure sleeve may have a concave contour toward the inside radially before being mounted on a component may be designed so that the contact surface for the sensor element on the pressure sleeve may have a convex contour toward the inside radially before assembly. This contour may be designed so that after assembly, at least the sensory system may be largely in flat contact with the contact surface.